In recent years, it has become popular to utilize a dispersed power source, which uses recyclable energy with a low impact on the environment, such as a solar power generation device and a wind energy conversion system. This kind of dispersed power source is configured so as to generate an AC power as the wind energy conversion system and a gas engine power generation device, or is configured so as to generate a DC power. Then, the power-generating capacity of the solar power generation device varies infinitely depending on fluctuation of amount of solar radiation. Therefore, it has been proposed to equalize a supply capability by means of combining the solar power generation device with an electrical power storage unit comprising a secondary battery.
Usually, the DC power generated in the dispersed power source, and the DC power outputted from the electrical power storage unit are converted into the AC power by using inverter equipment, and then the converted AC power is supplied to electrical devices, which are driven by the AC power. However, most of the electrical devices are configured to be driven by using an internal power circuit or an external wall adapter to convert the AC power into the DC power.
In the case where this kind of electrical devices are driven, the AC power is converted into the DC power by the internal power circuit or the external wall adapter after conversion of the DC power supplied from the dispersed power source and the electrical power storage unit into the AC power. Thus, the power loss increases with the power conversion, and the usage efficiency of the power decreases.
As a technology for solving this kind of problems, it has been proposed to use through a combination of the AC power supplied from a commercial power source and the DC power supplied from the dispersed power source and the electrical power storage unit in Japanese Patent Application Laid-Open No. 2002-315197 (hereinafter called “a document 1”). Then, an electricity distribution system is described in the document 1 and is provided with an AC feed line for supplying the AC power to a load and a DC feed line for supplying the DC power to a load.
By the way, the document 1 does not disclose the wiring configuration and the applied voltage to the electrical devices driven by the DC power (“DC load 12” described in the document 1). However, the document 1 discloses that when a supply voltage of the dispersed power source and the electrical power storage unit is within the range of 300 [V] to 345 [V], the system supplies the DC power supplied from the dispersed power source or the electrical power storage unit to a DC-DC converter (“DC/DC converter 18” described in the document 1). The DC-DC converter supplies the DC power to a DC load.
As described above, the configuration described in the document 1 requires the DC-DC converter for power conversion in order to supply the DC power to the electrical devices, and then the relatively-large power loss remains to be produced with the power conversion.
Then, the configuration described in the document 1 is provided with an AC-DC converter (“AC/DC converter 14 described in the document 1), for converting the AC power supplied from the commercial power source into the DC power, between the AC feed line and the DC feed line. It is considered that the output voltage of the AC-DC converter is set so as to roughly correspond to the output voltage of the dispersed power source or the electrical power storage unit. Therefore, for example, it is considered that the AC-DC converter outputs the DC voltage of about 300 [V].
On the other hand, it is preferred that a voltage to ground of each electrical circuit within a house is limited so as to be slightly higher than a maximum voltage of its electrical circuit. For instance, when the maximum voltage of each electrical circuit is 144 [V], the condition that the voltage to ground is less than or equal to 150 [V] is attached. Thus, the output voltage of the above-mentioned AC-DC converter can not satisfies this condition.